Wavelength division multiplexed (WDM) optical fiber communications systems transmit data on several optical carrier signals having different wavelengths. Typical prior art WDM systems use a separate optical signal source for generating each carrier signal. For example, a 1.times.N array of laser diode signal sources may be used to provide N carrier signals having different wavelengths. The carrier signal wavelengths are typically evenly spaced apart within the bandwidth of the optical fiber in which the signals are transmitted. Each laser diode is modulated by a different data stream so that N independent channels of information are provided.
There are a number of drawbacks associated with such multi-source systems. For example, each optical source typically requires active wavelength stabilization in order to prevent cross-talk or overlap between adjacent channel signals. Additional hardware and processing may be required for such stabilization. Furthermore, the complexity of individually-stabilized laser diode sources currently limits practical laser diode arrays to about 10 to 20 diodes. Additionally, the most efficient currently available photonic integrated circuits can be formed with only about four laser sources on a single chip. Packaging and source complexity constraints therefore represent a significant problem in present multi-source WDM applications. The complexity of each source also substantially increases the overall optical system cost. Although a large number of sources may permit large numbers of channels in principle, the aforementioned practical considerations presently limit the channel density of WDM systems to about 20 channels.
As such, a need exists for a single-source WDM system that avoids the cost, complexity and stabilization problems of the prior art.